1. Field of the Invention
The present invention relates to a semiconductor strain gauge that may be employed in various types of transducers such as motion sensing devices, scales and other instruments for measuring movements, forces and pressures, and more particularly to an improved semiconductor strain gauge wherein the semiconductor substrate includes at least one PN junction where both the P type and N type material is composed of amorphous semiconducting material.
2. Description of the Prior Art
The prior art contains many examples of strain gauges, i.e., a device that is used to measure displacement, forces or other physical phenomena which produce strain in the device. Once such type of strain gauge employs a strain sensitive metallic wire as the translating element. This element, when subjected to stress, undergoes a change in its overall electrical resistance. It is this change in resistance which is measured to thereby determine the magnitude of the applied force which has produced the stress. In an attempt to increase the sensitivity of these gauges (i.e., the change in resistance produced by the strain in the element) the use of crystalline semiconductor elements were adopted. It is well known that a semiconductor crystal with a specific direction of crystal axis exhibits a piezoresistive effect, i.e. a change in resistivity caused by an applied stress. This piezoresistive effect is part of the nature of the semiconductor material and has allowed crystalline semiconductor material to be used in strain gauges which are more effective than the gauges formed of a metallic material. In fact, it is well known that a semiconductor strain gauge utilizing the piezoresistive properties of a crystalline semiconductor material has an output sensitivity several ten's of times as high as that of a conventional metallic wire strain gauge. Examples of these semiconductor strain gauges can be found in U.S. Pat. Nos. 3,084,300; 3,312,790; 3,719,913; 3,673,354; 3,705,993; 3,922,705; 3,940,730; 4,047,144; 4,151,502; 4,203,327; 4,234,361 and 4,292,618.
Although strain gauges using crystalline semiconductor material represent a large improvement over the conventional strain gauge that employs a metallic wire, known crystalline semiconductor type gauges present certain disadvantages. For example, the crystalline semiconductor materials are very sensitive to impurities which often cause inaccuracies when used in a measuring device. These materials exhibit some problems with regard to their predictable resistance. Also, there are problems of reduced sensitivity when the semiconductor material is bonded via various bonding agents, e.g. organic resins, etc., to the material being strained. Furthermore, because of various difficulties that are encountered in controlling the curing of adhesives ordinarily used to bond the semiconductor material to the material being strained, inconsistent results are often obtained. Thus, known crystalline semiconductor strain gauges exhibit definite problems with respect to sensitivity, precision and reliability.